I do not see how you can use the jack you have to provide 5vthrough to the headphone. Luckily, you may not need the 5V. If you are trying to generate an interrupt when the headphones are not pluggedin, then it may work to connect the interrupt to pin 3 or 4.When the headphone is plugged-in, pins 3 & 4 are disconnected.Use a pull-down resistor to hold the interrupt pin 'off'.When the headphone is not plugged-in, then pin 3 will beconnected to pin 2 (right or left channel, does not matter).The signal from the WaveShield should trigger the interrupt.

yes, having removed the 5v from the headphone: it is louder and a good sound quality, but the interrupt,to start the file when inplugged and stopp it and rewind when unplugged doesn't function anymore.

when i in and unplug several time after another (like the installtaion should be used at the end) the file should play from the beginning each time, but doesn't.

yes. the sound was louder and better quality without having 5 v connected to the jack.

but the interrupt doesn't work anymore now: when inplugged the sound plays but doesn't stop and rewind when unplugged. after the second inplugg it doesnT play from the beginning on but from the middle somewhere.

It sounds as if you need a +5V on the interrupt pin to 'stop' the audio from the WaveShield. Also, you must GND the interrupt pin to 'start' the audio. Is this correct?

If that is the case, then you may be able to use a transistor (2N2222 or FET), diode and capacitator to make a integrator that will hold the interrupt pin at GND while there is audio but go to +5V when there is no audio.The problem I see is that the transistor may pull the interrupt pin to GND when you plug in the headphones but, without some experimenting, it may not.This means that when you un-plug your headphones it would stop the audio but, it may not start the playback when you plug-in your headphones.

If you have these common electronic parts you could give it a try.2n2222, 10K x3, 1N4148, 0.001uF